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Wave Corrector

Convert Vinyl Records and Tapes to CD & Digital Audio

Frequently Asked Questions - All FAQs

FAQs - All FAQs

If Wave Corrector doesn't completely remove a click, there are two possible procedures for manually removing it:

1. It may be possible to adjust the correction for the particular click. Depending on the characteristics of the click, Wave Corrector may underestimate its severity and hence under-correct it. To adjust the correction, first use the horizontal scale controls and the lower scroll bar to move to the point in the waveform where the click is occurring. Zoom in to about 50 samples per division. if you then double click with the mouse over the click, its correction will be selected in the correction list. You can now drag the edge of the correction with the mouse to widen it; and also use the left/right arrow keys to move the correction from side to side. Doing a combination of these things, you may be able to eliminate the pop. You can audition the effect of your adjustment using the ?Audition Corrected? toolbar button.

See the next question for a more detailed description.

2. It may be, if the click is very severe, that you cannot completely eliminate it with the above procedure. In this case, you can use 'Cut and Splice' to remove the click completely. To do this drag, with the mouse from left to right over the click. This will select the click as a block. Then use Block - Cut & Splice, to remove the click from the waveform. Note, before using Cut & Splice you can use the Audition Corrected toolbar button to audition the effect of the operation.

The easiest way to understand the Adjust/Insert procedure is to use it to adjust an existing correction (rather than inserting a new one).

Select a correction from the correction list, preferably a large yellow or red one. If the horizontal scale is sufficiently zoomed in, then you can adjust the correction as follows: move the mouse to the 'edge' of the correction; the mouse pointer will change to East-West arrows. Hold down the left mouse button and drag with the mouse. As you drag, the correction will become wider or narrower and you can see how the corrected wave changes versus the underlying uncorrected wave. Note, if the display is zoomed out too much, then you will not see the East-West arrows and you will have to invoke the command using the Adjust/Insert toolbar button. As well as adjusting the width of the correction, you can also move it to the left or right by using the cursor left/right keys. You will see how by adjusting the width and position of a correction, you can visually adjust the shape of the wave to get the best looking result; you can use the audition before and after toolbar buttons to hear the effect of your changes.

Having familiarised yourself with adjusting corrections, you can then move on to the slightly more complicated task of inserting new ones.

To insert a new correction, you need to visually identify the point in the waveform where the click is occurring. Sometimes this is obvious but other times it can be difficult and you need to use trial and error. Having identified the point where you think the click is, centre the display on that point and zoom in to say, 50 samples per division. (note, to centre the display you can simply double click over the point you want to centre on). Then, use the same procedure as described above to 'drag' a correction over the click. Again, you can use the audition commands to see if your correction has eliminated the click.

As a general rule, it is best not to perform multiple passes of the click corrector. This is because of the statistical method that Wave Corrector uses to discriminate between clicks and music. When it scans a waveform that has already been corrected, it is much more likely to trigger falsely. And if you continue to re-scan several times, eventually audible distortion will result.

However, for exceptionally noisy recordings, you can use Wave corrector's Super-Scan command to make multiple passes.

When you insert or adjust a correction, the program needs to have access to the waveform data in the vicinity of the correction. However, when you apply a filter, the waveform data is altered; and therefore it is not available for the insert/adjust commands. Hence, Insert/Adjust is disabled.

If you find you need to insert or adjust a correction after you've applied the rumble (or other) filter, then you need to use the 'Remove Filtering' command on the Waveform Menu. This will remove the filtering and re-enable Insert/Adjust. After you've made your insertions/adjustments you can then re-apply the filter.

Unfortunately, sensitivity levels 4 and 5 are quite aggressive and can cause distortion with certain types of music. Human voice can be affected as well as some low frequency brass and woodwind instruments. The most sensitive settings should therefore be used as sparingly as possible.

If you find that you definitely need to use setting 4 or 5 for most of the file, then you can use Wave Corrector Block commands to re-scan the distorted sections at a lower threshold. You simply need to drag a block over the section where distortion is occurring, and then select the command 'Re-Scan Block'. Select a lower setting (say 3) and the distortion should be removed. Of course, with the less aggressive setting, you may get the return of some of the noise. However, this will almost certainly be preferable to the distortion. Note, it is possible to manually insert corrections over clicks. So if re-scanning at level 3 causes some clicks to re-appear, you can try manually removing them. However, this is quite time consuming and requires a degree of skill/practice.

Wave Corrector is less effective against crackle than against other types of noise. The program is designed to restore vinyl recordings which generally contain discrete clicks rather than constant crackle. Crackle is more typical of old shellac records (78's). Unfortunately, crackle is a type of noise which is too continuous for click corrections to be totally effective; but it is too impulsive for a hiss filter to be effective. In Wave Corrector, clicks are detected by a statistical algorithm which analyses the music and looks for statistically significant departures from the norm. A constant background crackle makes it very difficult for this algorithm to differentiate between the music and the noise. On the other hand, the hiss filter assumes a smooth constant level of background noise (rather like when you de-tune an FM radio). Because crackle contains high amplitude instantaneous peaks, it cannot be completely removed by the hiss filer either. In fact, if you apply the hiss filter to crackly recording, the crackles may produce unpleasant artefacts.

The best approach for removing crackle is to Wave Corrector's SuperScan command to make multiple passes of the click corrector. This superimposes new corrections on top of those already present and will significantly reduce the crackle. It's probable however that some crackle will remain even after this process.

Note, crackle can be a by-product of inappropriate cleaning. This is because the cleaning process can leave behind microscopic residues. If you think this is the cause of your crackle, then you should have these residues removed by a professional record cleaning service.

These noises are typical of the artefacts you get when the hiss filter is working too hard. This can happen if the hiss filter has been incorrectly calibrated or if the noise present is not suitable for removal by a hiss filter.

The hiss filter is calibrated using a 'noise profile'. It is important to understand how this works if you are to avoid these unwanted artefacts. The 'noise profile' consists of a section of the recording where the noise is present but no music. The noise profile acts as a 'mask' which is subtracted from the rest of the recording. For the process to work properly, the original recording must include a second or two of lead-in or lead-out where there is no music playing. The program uses a portion of the lead-in or lead-out as the noise profile.

However, even when a lead-in is present, the program can still sometimes mis-measure the noise. For example, some live recordings can start with applause. In this case, the program may mistake the applause for noise and cause the program to assume the noise level is much higher than it really is. This in turn causes the filter to over-correct the hiss and the artefacts will then be much worse than they should be.

To avoid this, Wave Corrector provides the 'View Profile' and Capture New Profile' commands. Select the command View Profile on the Waveform menu and then use the Play Block command to verify that the profile is hiss only and that there is no musical content or applause or other sounds are present. If it is not genuine hiss, then you should manually capture a new noise profile as described in the Help file.

Another possible reason for filtering artefacts is if the noise is too spiky. The hiss filter is designed to remove tape hiss which is relatively constant broadband noise (like when you detune an FM radio) If you try to use the hiss filter, for example, on vinyl records, the characteristic of the noise is such that there are instantaneous peaks left behind after the filtering process. These also result in the warbling artefacts.